Infectious complications after vehicular trauma in the United States

Heme: The Lord of the Iron Ring

Heme is an iron-protoporphyrin complex with an essential physiologic function for all cells, especially for those in which heme is a key prosthetic group of proteins such as hemoglobin, myoglobin, and cytochromes of the mitochondria. However, it is also known that heme can participate in pro-oxidant and pro-inflammatory responses, leading to cytotoxicity in various tissues and organs such as the kidney, brain, heart, liver, and in immune cells. Indeed, heme, released as a result of tissue damage, can stimulate local and remote inflammatory reactions. These can initiate innate immune responses that, if left uncontrolled, can compound primary injuries and promote organ failure. In contrast, a cadre of heme receptors are arrayed on the plasma membrane that is designed either for heme import into the cell, or for the purpose of activating specific signaling pathways. Thus, free heme can serve either as a deleterious molecule, or one that can traffic and initiate highly specific cellular responses that are teleologically important for survival. Herein, we review heme metabolism and signaling pathways, including heme synthesis, degradation, and scavenging. We will focus on trauma and inflammatory diseases, including traumatic brain injury, trauma-related sepsis, cancer, and cardiovascular diseases where current work suggests that heme may be most important.

Trauma-induced heme release increases susceptibility to bacterial infection

Infection is a common complication of major trauma that causes significantly increased morbidity and mortality. The mechanisms, however, linking tissue injury to increased susceptibility to infection remain poorly understood. To study this relationship, we present a potentially novel murine model in which a major liver crush injury is followed by bacterial inoculation into the lung. We find that such tissue trauma both impaired bacterial clearance and was associated with significant elevations in plasma heme levels. While neutrophil (PMN) recruitment to the lung in response to Staphylococcus aureus was unchanged after trauma, PMN cleared bacteria poorly. Moreover, PMN show > 50% less expression of TLR2, which is responsible, in part, for bacterial recognition. Administration of heme effectively substituted for trauma. Finally, day 1 trauma patients (n = 9) showed similar elevations in free heme compared with that seen after murine liver injury, and circulating PMN showed similar TLR2 reduction compared with volunteers (n = 6). These findings correlate to high infection rates.

Evidence for Persistent Immune Suppression in Patients Who Develop Chronic Critical Illness After Sepsis

BACKGROUND

Many sepsis survivors develop chronic critical illness (CCI) and are assumed to be immunosuppressed, but there is limited clinical evidence to support this. We sought to determine whether the incidence of secondary infections and immunosuppressive biomarker profiles of patients with CCI differ from those with rapid recovery (RAP) after sepsis.

METHODS

This prospective observational study evaluated 88 critically ill patients with sepsis and 20 healthy controls. Cohorts were defined based on clinical trajectory (early death, RAP, or CCI), whereas immunosuppression was clinically determined by the presence of a postsepsis secondary infection. Serial blood samples were collected for absolute lymphocyte counts (ALCs), monocytic human leukocyte antigen-DR (mHLA-DR) expression, and plasma-soluble programmed death-ligand 1 (sPD-L1) concentrations.

RESULTS

Of the 88 patients with sepsis, 3 (3%) died within 14 days of sepsis onset, 50 (57%) experienced RAP, and 35 (40%) developed CCI. Compared with RAP patients, CCI patients exhibited a higher incidence and overall number of infections adjusted for hospital length of stay. ALC and mHLA-DR levels were dramatically reduced at the time of sepsis diagnosis when compared with healthy controls, whereas sPD-L1 concentrations were significantly elevated. There were no differences between RAP and CCI patients in ALC, sPD-L1, or mHLA-DR at the time of diagnosis or within 24 h after sepsis diagnosis. However, in contrast to the RAP group, CCI patients failed to exhibit any trend toward restoration of normal values of ALC, HLA-DR, and sPD-L1.

CONCLUSIONS

Septic patients demonstrate clinical and biological evidence to suggest they are immunosuppressed at the time of sepsis diagnosis. Those who develop CCI have a greater incidence of secondary infections and persistently aberrant markers of impaired host immunity, although measurements at the time of sepsis onset did not distinguish between subjects with RAP and CCI.

The Effect of Early Positive Cultures on Mortality in Ventilated Trauma Patients

BACKGROUND

The purpose was to examine the incidence of positive cultures in a highly susceptible subset of trauma patients admitted to the surgical intensive care unit (SICU) for mechanical ventilation and to examine the impact of their timing on outcomes.

PATIENTS AND METHODS

A retrospective review was conducted of blunt trauma patients admitted to the SICU for mechanical ventilation at a level I trauma center over a five-year period. All urine, blood, and sputum cultures were abstracted. Patients with at least one positive culture were compared with those with negative or no cultures. The primary outcome was mortality. A Cox regression model with a time-dependent variable was utilized to calculate the adjusted hazard ratio (AHR).

RESULTS

The median age of 635 patients meeting inclusion criteria was 46 and 74.2% were male. A total of 298 patients (46.9%) had at least one positive culture, with 28.9% occurring within two days of admission. Patients with positive cultures were more likely to be severely injured with an injury severity score (ISS) ≥16 (68.5% vs. 45.1%, p < 0.001). Overall mortality was 22%. Patients who had their first positive culture within two and three days from admission had a significantly higher AHR for mortality (AHR: 14.46, p < 0.001 and AHR: 10.59, p = 0.028, respectively) compared to patients with a positive culture at day six or later.

CONCLUSIONS

Early positive cultures are common among trauma patients requiring mechanical ventilation and are associated with higher mortality. Early identification with "damage control cultures" obtained on admission to aid with early targeted treatment might be justified.

Urinary tract infection in elderly trauma patients: review of the Trauma Quality Improvement Program identifies the population at risk

BACKGROUND

Elderly trauma patients are at high risk for urinary tract infection (UTI). Despite this, UTI has been deemed a potentially preventable problem and therefore not reimbursable by the Centers for Medicare and Medicaid Services. Early identification of UTI in these patients should lead to prompt treatment, improved outcomes, and cost savings. Risk factors for UTI development in this population must be elucidated to realize these goals.

METHODS

The Trauma Quality Improvement Program (TQIP) database was used to analyze elderly patients (≥65 years) admitted as a result of injury during 2011. Patients with genitourinary injuries or undergoing dialysis before admission were excluded. Multivariable logistic regression analysis was conducted to identify UTI risk factors. Mean cost of UTI was calculated based on the assumption of $862 to $1,007 per UTI.

RESULTS

In total, 33,257 patients were identified; 1,492 developed UTI (4.5%). Multiple significant risk factors were identified, including age greater than 75 years, female sex, ascites, moderate head injury, impaired sensorium, congestive heart failure, and duration of hospital stay (all p < 0.05). Assuming that UTIs diagnosed on hospital Day 1 were preexisting, the cost of UTI to TQIP hospitals ranged from $1,280,959 to $1,496,434 per year.

CONCLUSION

Duration of stay has a profound impact on the development of UTIs in elderly trauma patients, but overall severity of injury does not. In addition, multiple nonmodifiable risk factors were identified, prompting the possibility for increased screening of occult UTIs. Reimbursement for care of UTI in this complicated patient population should be revisited. The TQIP database must improve urinary catheter data.

LEVEL OF EVIDENCE

Epidemiologic study, level III.

Nosocomial infections after severe trauma are associated with lower apolipoproteins B and AII

BACKGROUND

Infection after severe trauma is a significant cause of morbidity and mortality days to weeks after the initial injury. Apolipoproteins play important roles in host defense and circulating concentrations are altered by the acute inflammatory response. The purpose of this study was to determine if patients who acquire infection after severe trauma have significantly lower apolipoprotein levels than trauma patients who do not become infected.

METHODS

We conducted a case-control study on a prospectively identified cohort of adult patients admitted to our intensive care unit after severe trauma (Injury Severity Score ≥ 16). We compared plasma apolipoprotein levels between patients who acquired an infection within 30 days after trauma (cases) and those that remained infection free (controls).

RESULTS

Of 40 patients experiencing severe trauma, we identified 22 cases that developed an infection within 30 days after injury. Cases had significantly lower posttrauma plasma levels of apolipoprotein B (p = 0.02) and apolipoprotein AII (p = 0.02) compared with controls. Consistent with previous studies, cases also received greater volumes of crystalloid infusions (p < 0.01) and blood transfusions (p < 0.01). Cases also had a more profound inflammatory response as measured by interleukin 6 levels (p = 0.02).

CONCLUSION

Infection after severe trauma is associated with decreased circulating apolipoproteins as compared with uninfected controls. Profoundly decreased plasma apolipoproteins B and AII could potentially contribute to the impaired immunity after severe trauma. Apolipoproteins are potential targets for identifying those patients at risk of infection after trauma and for interventions aimed at preventing nosocomial infections.

LEVEL OF EVIDENCE

Prognostic study, level III.